1. Field of the Invention
The present invention relates generally to an automotive transmission and more specifically to a planetary gear transmission which increases both the longevity and the efficiency of same.
2. Description of the Prior Art
FIG. 1 of the drawings schematically shows a previously proposed planetary gear transmission. This arrangement includes sun gears S1 and S2, ring gears R1 and R2 and pinion carriers PC1 and PC2 on which pinion gears are mounted connected, as shown with the input shaft I, output shaft O, first-fourth clutches (C1, C2, C3 and C4), two brakes (B1 and B2) and two one-way clutches OWC1 and OWC2. With this arrangement the clutches and brakes are selectively applied as shown in the table of FIG. 2 to produce four forward speeds and one reverse.
However, with the above described arrangement the engine torque is applied via input shaft I to the sun gear S1 by way of clutch C3 and one-way clutches OWC1 and OWC2 in first second and third speeds and to sun gear S2 through clutch C3 in reverse. This induces the problem that, as the diameter of the sun gears S1 and S2 are relatively small, a relatively large stress is applied to the teeth thereof, thus inducing a limit to which torque can be safely applied. Further, as the sun gear S1 tends to rotate at a speed approximately 2.5 times that of the input shaft during fourth speed a further problem is encountered in that, due to the prolonged high rotational speeds to which the element is subjected, the structural strength of the components associated with the sun gears along with the durability of the bearings which support same must be given particular attention to avoid rapid deterioration of the transmission as a whole. Moreover, the arrangement of this gear train is such as to permit a closed loop transmission path to be established between the two planetary gear sets inducing both mechanical inefficiency and unnecessary wear of the two planetary gear units.